Conventionally, in manufacture of such glass panel, paste-like low melting point glass is applied to peripheries of both of the glass plates and heated to 480° C. or more as shown in FIG. 6 to melt the low melting point glass. Thereafter, the glass is cooled to room temperature and solidified to execute the joining process for sealing and joining the glass plates at the peripheries thereof.
Then, the void defined between the glass plates and the low melting point glass which have been cooled to room temperature are heated again to about 200° C. for drawing and removing the gas from the void to execute the baking process.
Since the baking process has conventionally been executed at the temperature around 200° C., there have been disadvantages as follows.
As illustrated in FIG. 7, atmospheric pressure acts on surfaces of the glass plates 1A and 2A when the gas is drawn and removed from the void defined between the glass plates. The low melting point glass 4A is in a generally hardened condition at the temperature around 200° C. as in the conventional method, specifically the temperature around 200° C. established by reheating the glass after the glass is once cooled to room temperature. As a result, the glass plates 1A and 2A undergo an internal stress as shown in arrows (solid lines) to bulge and bend toward the void V, which decreases the strength of the glass plates 1A and 2A. In an extreme case, the glass plates 1A and 2A bear the internal stress at end portions thereof as shown in arrows (broken lines) to bend outwardly, which leads to a drawback that the glass plates 1A and 2A easily break around the end portions thereof.
The glass plates 1A and 2A are heated to 480° C. or more when the joining process is executed for joining the glass plates. Thus, inorganic substances including Na are generated from the glass plates 1A and 2A. Also, organic substances are generated from a binder mixed into the low melting point glass 4A. These inorganic and organic substances adhere to inner surfaces of the glass plates 1A and 2A. These substances are not completely drawn and removed from the void by the baking process executed at the temperature around 200° C., and remain adhering to the inner surfaces of the glass plates 1A and 2A. As a result, the quality of the glass panel could be lowered.
Specifically, when the glass plates 1A and 2A comprise special glass with a special coating having a heat-absorbing or ultraviolet-absorbing function applied to the inner surfaces thereof, the inorganic or organic substances may remain in and adhere to flaws in the coating on the inner surfaces thereof. As a result, the flaws of the coating become noticeable to cause a significant quality deterioration.
The present invention has been made having regard to the conventional problems as described above, and its object is to minimize an internal stress generated in the glass plates, when a baking process is executed, to prevent a decline in strength. Another object of the invention is to provide a method of manufacturing a glass panel capable of restraining inorganic and organic substances from remaining in a void defined between the glass plates to the utmost to prevent deterioration in quality.